A CONCEPTUAL FAIRWEATHER STORM MODEL OF BEACH NEARSHORE PROFILE EVOLUTION AT DUCK, NORTH-CAROLINA, USA

Limited long-term (decadal) beach-nearshore profile observations sugge st that during fairweather conditions, the beach-nearshore slope gradu ally steepens while the shoreline remains relatively stable. The steep ening process is terminated by an extreme storm event during which san d is carried offshore, the shoreline migrates landward and the beach-n earshore slope flattens. When the interval between storms is large, th e profile approaches a maximum steepness and its susceptibility to ero sion and shoreline recession is maximized. To test this conceptual fai rweather/storm model, storm events were related to shoreline position, sediment volume and slope changes obtained from the high precision pr ofile data at Duck, North Carolina Beach-nearshore profiles have been collected for 10 1/2 years at approximately biweekly intervals. Four m ajor groups of storms occurred during the observation period. They all caused an abrupt increase in the volume of the upper shoreface; in tw o cases there was a net volume gain to the overall profile. During int ervening fairweather conditions, there was a steady onshore transport of sand from the upper shoreface while the total volume remained const ant. Slope changes, determined by linear regression of the upper shore face, support the conceptual fairweather/storm model. Inclusion of the more landward element of the profile was difficult due to the presenc e of bars. The shoreline at Duck was insensitive to these offshore cha nges due to the coarse grain sire at the shoreline. However, other sit es composed of finer-grained sediments might be expected to more sensi tive to such changes. These results show that the fairweather/storm mo del may be a useful conceptual tool to examine medium- to long-term (y ears to many decades) beach-nearshore profile behavior.